Vapour generator for ship propulsion unit



Jan. 23, 1968 E. e. HUTCHINGS 3,

VAPOUR GENERATOR FOR SHIP PROPULSION UNIT Filed March 14 1966 3 Sheets-Sheet 1 Fig.1. 4

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United States Patent 3,364,904 VAPOUR GENERATOR FOR SHIP PROPULSION UNIT Edward G. Hutchings, Wembley, England, assignor to Babcock & Wilcox, Limited, London, England, a corporation of Great Britain Filed Mar. 14, 1966, Ser. No. 534,024 Claims priority, application Great Britain, Mar. 15, 1965, 10,925/65 Claims. (Cl. 122-480) ABSTRACT OF THE DISCLOSURE A vapor generator adapted to supply superheat and reheat steam. The generator includes a furnace chamber and two gas passes arranged for parallel flow of combustion gases therethrough. One of the passes contains the reheater and a portion of the superheater heat exchange tubes while the other pass contains the remainder of the superheater tubes. Each of the two passes is equipped o This invention relates to ship propulsionpower plant and particularly to the boilers of such plants.

-In order to obtain efiicient operation in a steam turbine ship propulsion plant, high temperature of superheat with reheating of the steam between stages is desirable. Reheating, however, tends to lead to complications since both the temperature of superheat and the temperature of reheat must be maintained at safe and acceptable values during normal ahead operation, while during as-tern operation since the turbine brought into use for the purpose usually requires no reheat measures must be taken to guard against damage to the reheater by overheating.

Copending application Ser. No. 399,312 filed Sept. 1964, and now Patent No. 3,280,559, provides in a ship propulsion power plant a tubulous vapour generator adapted to supply superheated vapour to an engine and to reheat the vapour between engine stages. The generator has parallel gas passes leading from a furnace chamber, a first section of superheater in one pass, a reheater in a second pass and, for affording protection to the reheater when during operation vapour flow through the reheater is discontinued, damper means for controlling the flow of gases from the furnace chamber through the second pass, and a second section of superheater disposed within the second pass between the furnace chamber and the reheater.

With such distribution of the superheater heat exchange surfaces the second section of the superheater exerts a cooling action on gases that may flow into the second pass when the dampers associated with that pass are closed and before such gases can reach the reheater heat exchange surfaces; moreover, with variation in the distribution of gas flow between the passes the variation in the final temperature of superheat is less than that which would occur were the whole of the superheater heat exchange surfaces to be disposed within the first pass.

The object of the present invention is to provide such a vapour generator or a modification of such a vapour generator in a marine power plant which is more particularly adapted to operate with an advantageous degree of 3,364,904 Patented Jan. 23, 1968 stability of superheat and advantageous superheat temperatures, while permitting with safety the use, if desired, of a relatively small amount of superheating surface upstream, as regards heating gas flow, of the reheater.

The present invention comprises, in a ship propulsion unit, a vapour generator adapted to supply superheated vapour to an engine and to reheat the vapour between engine stages. The vapour generator includes a furnace chamber, and first and second gas passes arranged for the flow in parallel therethrough of combustion gases generated in the furnace chamber. Both a final section of a superheater and an initial or an intermediate section of the superheater are disposed in the first gas pass. A reheater and, upstream as regards gas flow of the reheater, either the remaining intermediate section or the remaining initial section of the superheater are disposed in the second gas pass. Damper means are provided to proportion the flow of combustion gases between the first and second gas passes. Disposed in a superheated vapour conduit between two superheater sect-ions subsequent in the vapour path to a superheater section in the first pass, are attemperator means capable of increased performance with increased temperature of vapour entering the attemperator means.

The invention will now be described by way of example with reference to the accompanying drawings, in which:

FIGURE 1 is an elevation, in section on the line II of FEGUR E 2, of a marine reheat boiler,

FIGURE 2 is an elevation of the boiler in section on the line 11-11 of FIGURE 1,

FIGURE 3 is a sectional plan view of a boiler drum to show a-ttemporator coils therein, and

FIGURES 4 to 6 diagrammatically illustrate certain modifications of the steam flow in relation to the tube banks in the gas passes.

Referring to FIGURES 1 to 3 of the drawings, a marine steam boiler includes a furnace chamber 1, the walls of which are lined with vapour generating tubes 2, which is flanked by first and second gas passes 3 and 4 which are upright and have gas inlets Sand 6 respectively at their lower ends. The furnace chamber is formed in its roof with burner ports at positions 7 fitted with oil burners (not shown) of known atomizing types.

The two gas passes mentioned are both at the rear of the furnace chamber. Thus the boiler setting is divided by a transverse tube wall 8 separating the furnace cham her 1 at the front of the setting from the up-fiow passes 3 and 4 at the rear of the setting. The tubes 9 in the tube wall 8 extend upwardly from a first lower header 10 initially in staggered relationship to define a screen 11 of spaced tube limbs at the entry from the furnace chamber to a space 12 below the two gas passes and then continue vertically as a single row to terminate at their upper ends in an upper header 13. A second set of tubes 14 extends from the first header 10 forwardly at an upward inclination to define the floor 15 of the furnace chamber, then vertically to define the front wall 21 of the setting to an upper header 22. A third set of tubes 23 extends from the first lower header 10 rearwardly at an upward inclination to define the floor 24 of the space 12, then vertically, defining the rear wall 25 of the setting to an upper header 26 in which the tubes terminate. The outer side Walls 27 of the up-flow gas passes are defined by tubes 28 extending vertically from respective second and third lower headers 29 to the level of the steam and water separator drum 30 of the boiler, Where they extend in spaced relationship across respective gas outlet passages 31 and 32 from the passes 3 and 4 to discharge directly to the centrally disposed separator drum 30. Further tubes 33 from the second and third lower headers extend vertically to define the side walls 34 of the furnace chamher and then extend inwardly at an upward inclination to an upper header 35, discharging to the separator drum, to define the roof 41 of the furnace chamber. The various walls are suitably insulated and an outside casing 42 is provided, there being a space between the said casing and the various water walls through which combustion air may be circulated and which at the rear of the setting accommodates the superheater, reheater, and economizer headers to be mentioned.

The gas passes 3 and 4 are separated from one another by a tubulous wall 43 extending between the wall 8 at the front of the passes and the wall 25 at the rear of the passes. The tubes of the wall extend from the second and third lower headers initially vertically in the outer sidewalls 27 and then in spaced relationship inwardly and upwardly as respective screens 44 and 45 across the gas sections and 6 of the first and second gas passes to the base of the tubulous wall 43 and then extend vertically to connect directly into the separator drum 30. The gas outlet passages 31 and 32 lead to the location above the separator drum where the gases enter respective gas off-takes 46 and 47 in which respective control dampers 48 and 49 of the gas passes 3 and 4 are located. Suitably the tubulous wall 43 is a membrane wall. The transverse tubewall 8 and the other tubulous walls of the setting may also be membrane walls. Connectors 50 lead from the upper headers 13, 22, 26 and 35 into the drum 30.

The superheater is in three sections connected for serial flow of vapour therethrough, of which the intermediate superheater section 51 is disposed at the lower end of the first pass and consists of a bank of horizontal, sinuous tubes extending forwardly and rearwardly across the gas pass, said bankbeing supplied from a lower steam inlet header 52 and delivering to an upper steam outlet header 53. Above the intermediate superheater section 51 is the final superheater section 61 consisting of a bank of horizontal sinuous tubes extending forwardly and reanwardly across the first gas pass, said bank being supplied from a lower steam inlet header 62 and delivering to an upper steam outer header 63. Above the final superheater section is an economizer section 64 formed of banks of sinuous tubes also extending forwardly and rearwardly across the gas pass, said section being supplied with water from a lower water inlet heater 65 and delivering to the drum 30.

The heat exchange tubes in the second gas pass similarly extend forwardly and rearwardly and comprise the sinuous tubes of the initial superheater section 66 disposed at the bottom of the gas pass and sinuous nested tubes of reheater tube banks 67 above the initial superheater section. The initial superheater section receives steam through a lower steam inlet header 68 and delivers to an upper steam outlet header 69. The reheater 67 receives steam from an upper steam inlet header 70 and delivers to a lower steam outlet header 71.

The separator drum may be provided internally thereof with cyclone separators (not shown) suitable downcomers 72 extend from the end lengths of the drum and are provided for supplying water to the first, second and third lower headers and 29.

As stated, the initial, intermediate and final superheater sections are connected for serial flow of steam therethrough. Connecting the intermediate andvfinal superheater sections is a steam conduit 73 having an attemperator 74 therein. The attemperator comprises a heat exchanger 81 in a steam path 82 controlled by a valve 83 and a bypass steam path 84 in parallel with the path 82 and controlled by a valve 85. The heat exchanger 81 is formed by a plurality of coils in loop form connected for the flow of steam therethrough in parallel and externally cooled by boiler water. For example, the coils may extend as shown in FIGURE 3 within the water space of the drum 30 or they may extend within a vessel separate from the drum 30 but provided with connections to the boiler so that the coils may be cooled by boiler water.

In the operation of the boiler to generate and super heat steam for the high pressure stage of a steam turbine for ahead drive of the ships power plant and to reheat steam between the high and low pressure stages of the turbine, combustion gases generated in the furnace chamber 1 by the combustion of fuel oil delivered in atomized spray form by the burners in the furnace chamber roof 41 leave the bottom of the furnace chamber, enter-the space 12 below the two gas passes 3 and 4 and flow in parallel gas streams upwardly through the two gas passes. Water to be delivered to the drum 30 to maintain the Water level therein is first heated in the economizer 64. Steam is generated in the various floor, screen and Wall tubes and passes with water into the drum in which steam and water separation is effected with the aid of cyclone separators (not shown). The downcomers 72 take water from the drum to supply the various steam-generating tubes. A conduit (not shown) takes steam from the drum to the first superheater section 66. After passing through the first superheater section, the steam is led by another conduit (not shown) to the intermediate superheater section 51. After passing through the intermediate superheater section, the steam is led by the conduit 73 through the attemperator 74 comprising the attemperator coils 81 in the drum 30 together with the attemperator coil bypass 84, to the final superheater section 64. Afterpassing through the final superheater section the steam is led to the high pressure stage of the ahead turbine. After expansion in the said turbine stage, the steam is led to the reheater 67. After passing through the reheater it is led to the low pressure stage of the ahead turbine for further expansion therein.

The dampers 48 and 49 are adjusted relative to one another so as to proportion the total gas flow between the first and second pass that the temperature of the re heated steam has the desired value. In order to ensure also the minimum draft loss through the boiler, the necessary gas flow proportioning is achieved by partially closing the dampers 48 of the first pass with the dampers 49 of the second pass fully open, or by partially closing the dampers 49 of the second pass with the dampers 48 of the first pass fully open.

When a change is made in the power to be delivered by the ahead turbine, the load on the boiler is changed accordingly. By reason of the change in the temperature of the steam to be reheated, of the change in the temperature of the gases leaving the furnace chamber, and of the change in the gas mass flow over the reheater, the temperature of the reheated steam tends to alter. Manually, by reference to an indication of the reheated steam temperature, or automatically in dependence upon a measure of reheated steam temperature, an appropriate readjustment of the dampers 48 of the first pass or/and of the dampers 49 of the second pass is made to regulate the reheated steam temperature.

If, at a given boiler load, the gas flow in the first gas pass 3 were to be increased while the gas flow in the second gas pass 4 was correspondingly reduced, the initial superheater section 66 would be less greatly heated while the intermediate and final superheater sections 51 and 61 would be more greatly heated. Since the initial superheater section 66 has a heat exchange area which is limited in order that the reheater 67 may readily receive adequately hot gases in normal operations, the reduction in heat absorption in the primary superheater section will be less than the increase in heat absorption by the intermediate and final superheater sections 51 and 61; however, more heat will be abstracted from the steam by the attemperator 74 which receives hotter steam and therefore the final steam temperatiire may not greatly vary. Similar but reverse considerations apply for the case of the opposite re-proportioning of the gas flow between the passes. If, with unchanged damper settings, the load were to be increased or decreased, the heat absorptions per pound of steam in the superheater sections would increase or decrease respectively, however, the attemperator, receiving hotter or cooler steam respectively, will abstract respectively more or less heat per pound of steam and the change in the final superheat temperature will be limited. It follows that during normal operation superheat temperature may be regulated by damper adjustments as may be necessary for the purpose without the occurrence of excessive changes in final superheat temperature although the settings of the valves 83 and 85 of the attemperator may be fixed. Moreover, the final superheater section, receiving attemperated steam, is protected.

In the operation of the boiler to generate and superheat steam for the steam turbine for astern drive of the ships power plant, which so-called reversing turbine requires no reheated steam, the furnace chamber 1 is fired to generate the required amount of steam at the required pressure while the dampers 49 of the second gas pass 4 are closed. The initial superheater section 66 is traversed by saturated or low temperature steam on its way to the intermediate superheater section 51 and by cooling any gases that may flow from the space 12 into the second gas pass 4 it protects the reheater 67, in which no steam is flowing. Substantially all the gases flow, however, through the first gas pass 3 in which the intermediate and final superheater sections 51 and 61 are disposed and in the gas quantities that will usually be required to give relatively high heating to the second and third superheater sections. In the attemperator 74, receiving relatively hot steam from the intermediate superheater section 51, there will be relatively large temperature differences requiring a relatively large withdrawal of heat from the steam between the said two superheater sections in order to limit the final steam temperature as well as to the avoid overheating of the final superheater section 61.

It will be understood that the capacity of the attemperator coils 81 and the settings of the valves 83 and 85, the gas flow path areas and the disposition of the superheater tubes in the gas passes will be chosen in relation to one another so that the reheater may be adequately heated, and so that the reheat temperature may be regulated as described and the superheat temperature may be stabilized with a restriction on it maximum under the conditions for astern operation.

If the expected limited steam temperature variations are unacceptable, a further indirect-contact-type attemperator having fixed valve setting may be placed in the steam conduit from the final superheater section, which attemperator will further restrict temperature variations.

The superheat temperature may be controllably regallated if desired with the aid of a spray-type attemperator which is disposed in the steam conduit from the final superheater section and which is automatically controlled in dependance upon the temperature in the conduit subsequent thereto. In view of the described limitations in the variations of steam temperature the capacity of said attemperator may be relatively small. The use of two attemperators does not lead to control difiiculties if, as envisaged, the indirect-contact-type attemperator 74 is normally used with pre-set fixed valve settings.

Alternatively, the superheat temperature may be regulated with the aid of gas bypass to the first and second gas passes. For example, referring to FIGURE 4, in which items bearing the same reference numerals as items in FIGURE 1 to 3 have corresponding respective functions, between the first and second gas passes 3 and 4 may be arranged a third upflow gas pass 101 which is separated from the first and second gas passes by respective partition walls and in which the gas flow is controllable by the operation of dampers 102. In the third gas pass there may he no heat exchange means; alternatively, heat exchange means 103 may be provided therein which may be economizer or steam generating surfaces. A readjustment of the dampers of the third pass to a more open position or to a more closed position will tend respectively to reduce or to increase final superheat temperature, and the posi- '6 tioning of said dampers may be controlled automatically to regulate said temperature.

As described and indicated, the steam in each of the superheater sections flows generally upwardly therein, that is to say, in parallel flow with the gas passing over the section. However, if known considerations such as the degree of superheat to be provided, the space available and the cost of heat resistant tubes so indicate, the steam may be led through any or all of the superheater sections in counterflow to the gas.

FIGURE 5 indicates a modification in which the initial superheater section 66 is placed in the second gas pass 4 below the reheater 67 and the intermediate superheater section 51 is placed in the first gas pass 3 below the economizer 64 and above the final superheater section 61; the attemperator 74 is placed in the steam flow between the intermediate and final superheater sections.

FIGURE 6 indicates a modification in which the initial superheater section 66 is placed in the first gas pass 3 be low the economizer 64 and above the final superheater section 61 and the intermediate superheater section 51 is placed in the second gas pass 4 below the reheater 67; the attemperator 74 is placed in steam fiow between the initial and intermediate superheater sections. Alternatively, it may be satisfactory to place the attemperator in the steam flow between the intermediate and final superheater sections.

In another modification (not shown) the final superheater section is placed in the first gas pass below the economizer and above the initial superheater section and the intermediate superheater section is placed in the second gas pass below the reheater; the attemperator is placed in the steam flow between the initial and intermediate superheater sections or in the steam flow between the intermediate and final superheater sections.

It will be understood that in any of the arrangements indicated heat exchange surfaces additional to those mentioned may be incorporated as may be suitable in view of the gas temperatures to be expected, the designed duty of the boiler and the space available. For example further economizer surface maybe placed in the second gas pass above the reheater, or, as indicated in the boiler specifically described in the aforementioned copending application, an initial reheating tube bank may be placed in a common gas passage above the dampers or, alternatively or in addition, economizer surface might be placed in such common gas passage.

I claim:

1. In a ship propulsion system wherein means are provided to selectively supply superheated and reheated vapour to a forward drive turbine and only superheated vapour to an astern drive turbine, the combination with said propulsion system of a Vapour generator comprising walls defining a furnace chamber, means for burning fuel in said furnace chamber to produce high temperature heating gases, means defining a first gas pass connected for the flow therethrough of high temperature gases from said furnace chamber, means defining a second gas pass con nected for the flow therethrough of high temperature gases from said furnace chamber, damper means arranged to regulate the flow of heating gases through said first and second gas passes, a pair of superheater sections disposed in said first gas pass, an additional superheater section and a reheater section disposed in said second gas pass, said additional superheater section being arranged upstream of said heheater section with respect to gas flow through said second gas pass, vapour conducting conduits connecting the three mentioned superheater sections for serial flow of vapour therethrough, the three mentioned superheater sections including an initial section an intermediate section and a final section, the final section being disposed in said first gas pass, and vapour attemperating means responsive to the temperature of the vapour entering said attemperating means disposed in one of said vapour conducting conduits which connects two of said superheater sections and in which there flows vapour that has passed through the superheater section in the first gas pass other than said final section.

2. The invention according to claim 1 wherein said first and second gas passes are arranged for parallel flow of heating gases therethrough, and said attemperator means includes a heat exchanger, means for passing liquid from said vapour generator in heat exchange relation with the vapour flowing through said heat exchanger, and means for by-passing vapour around said heat exchanger.

3. The invention according to claim 2 wherein said heat exchanger is of the indirect type.

4. The invention according to claim 3 wherein there is provided means for regulating the vapour temperature leaving the final superheater section.

5. The invention according to claim 4 wherein the means for regulating the vapour temperature leaving the final superheater section includes a vapour conducting conduit for passage of vapour from said final superheater section, and means for spraying liquid directly into the vapour passing through the last mentioned conduit.

6. The invention according to claim 2 further including means defining a third gas pass connected for the controllable flow therethrough of high temperature gases from said furnace chamber, said third gas pass being arranged in parallel flow relation with said first and second gas passes to enable by-passing of gases around said first and second gas passes. a V

7. The invention according to claim 1 wherein said initial section is disposed in said second gas pass.

8. The invention according to claim 7 wherein said intermediate section is disposed in said first gas pass upstream of said final section with respect to gas flow through said first gas pass.

'9. The invention according to claim 1 wherein said final section is disposed in said first gas pass upstream of the other superheater section disposed in said first gas pass with respect to gas flow therethrough.

10. The invention according to claim 9 wherein the initial section is disposed in said second gas pass.

References Cited UNITED STATES PATENTS 3,048,017 8/1962 Mary 6()73 X 3,280,559 10/1966 Hutchings 60-73 KENNETH W. SPRAGUE, Primary Examiner. 

